1. Field of the Invention
This invention relates to novel organo-1-oxa-4-azonium cyclohexane compounds, a process for preparing the quaternary ammonium salts, and the use of the quaternary ammonium salts in the synthesis of zeolitic molecular sieves. The process involves forming 1-oxa-4-azoniumcyclohexane compounds from suitable reagents such as a substituted alkane and 1-oxa-4-azacyclohexane derivatives.
2. Description of the Related Art
Classes of molecular sieves include crystalline aluminophosphate, silicoaluminophosphate, or metalloaluminophosphate compositions which are microporous and which are formed from corner sharing AlO4/2 and PO4/2 tetrahedra. This class is described by Lok and coworkers in U.S. Pat. No. 4,440,871. Other classes of molecular sieves include crystalline aluminosilicate or silicate compositions, often referred to as zeolites. These are formed from corner sharing SiO4/2 and AlO4/2 tetrahedra. Numerous molecular sieves, both naturally occurring and synthetically prepared, are used in various industrial processes. Synthetically, these molecular sieves are prepared via hydrothermal synthesis employing suitable sources of Si, Al, P, and structure directing agents such as alkali metals, alkaline earth metals, amines, or organoammonium cations. The structure directing agents reside in the pores of the molecular sieve and are largely responsible for the particular structure that is ultimately formed. These species may balance the framework charge associated with silicon or other metals such as Zn in the aluminophosphate compositions or aluminum in the silicate compositions and can also serve as space fillers to stabilize the tetrahedral network framework. Molecular sieves are characterized by having pore openings of uniform dimensions, having a significant ion exchange capacity, and being capable of reversibly desorbing an adsorbed phase which is dispersed throughout the internal voids of the crystal without significantly displacing any atoms which make up the permanent molecular sieve crystal structure. Molecular sieves can be used as catalysts for hydrocarbon conversion reactions, which can take place on outside surfaces as well as on internal surfaces within the pore.
Synthesis of molecular sieve materials often relies on the use of organoammonium templates known as organic structure directing agents (OSDAs). While simple OSDAs such as tetramethylammonium, tetraethylammonium and tetrapropylammonium are commercially available, often, OSDAs are complicated molecules that are difficult and expensive to synthesize; however, their importance lies in their ability to impart aspects of their structural features to the molecular sieve to yield a desirable pore structure. For example, the synthesis of N,N,N,-trimethylmyrtanylammonium derivatives allowed the synthesis of CIT-1, a member of the CON zeotype (Lobo and Davis J. Am. Chem. Soc. 1995, 117, 3766-79), the synthesis of a methyl substituted N,N,N′,N′-tetraethylbicyclo[2.2.2]oct-7-ene-2,3,5,6-dipyrrolidinium diiodide enabled the synthesis of ITQ-37, the member of the ITV zeotype (Sun, et. al. Nature, 2009, 458, 1154-7) and synthesis of the trans isomer of N,N-diethyl-2-methyldecahydroquinolinium iodide (Elomari, et. al. Micro. Meso. Mater. 2009, 118, 325-33) allowed synthesis of SSZ-56, the member of the SFS zeotype. The use of 1,4,7,10,13,16-hexamethyl-1,4,7,10,13,16-hexaazacyclooctadecane as OSDA has been shown to allow synthesis of STA-7, an aluminophosphate based material of the SAV zeotype (Wright, et. al. J. Chem. Soc., Dalton Trans., 2000, 1243-1248).
The art clearly shows that use of complex organoammonium SDAs often results in new molecular sieve materials. However, the synthesis of these complicated organoammonium compounds is quite lengthy and requires many steps, often in an organic solvent, thereby hindering development of the new molecular sieve material. Frequently, even for simple, commercially available OSDAs, the OSDA is the most costly ingredient used in synthesizing molecular sieve materials. Consequently, it would be economically advantageous to synthesize new molecular sieves from either commercially available organoammonium SDAs or SDAs which may be readily synthesized from commercially available starting materials.
The simple, commercially available, amine morpholine (tetrahydro-1,4-oxazine has been previously utilized in aluminophosphate based molecular sieve synthesis and has been shown to yield CHA-type molecular sieves (Marchese, et. al. Micro. Meso. Mater. 1999, 30, 145-53; Ito, et. al. Acta Cryst. 1985, C41, 1698-1700) in aluminophosphate based syntheses, but has not yet been shown to yield other structure type molecular sieves. Additionally, the vapor pressure of morpholine is relatively high, making its use on commercial scale troublesome as low vapor pressure organoammonium SDAs are preferred.
The complicated OSDA(s) discussed previously were synthesized ex-situ and added to the reaction mixture at several points. However, one drawback of ex-situ synthesis is the process is typically carried out in the presence of an organic solvent, which necessitates at least one undesirable purification step to recover the SDA from the unwanted organic material.
Therefore, what is needed in the art are novel organo-1-oxa-4-azonium cyclohexane compounds. It would be desirable for these organo-1-oxa-4-azonium cyclohexane compounds to be useful as SDAs for aluminosilicate, silicate, aluminophosphate, or silicoaluminophosphate compositions.